Biodegradable laminate sheet and molded item from biodegradable laminate sheet

ABSTRACT

A biodegradable laminate sheet having as its object to provide a formed body superior in heat resistance, shock resistance, transparency and formability, and having non-stretched polylactic acid-family resin layer of which the crystallinity is 20% or less, and a layer comprising a biodegradable resin other than a polylactic acid-family resin.

TECHNICAL FIELD

The present invention relates to a biodegradable laminate sheet of apolylactic acid-family resin which can be formed by various formingssuch as vacuum forming, air-pressure forming, vacuum air-pressureforming and press forming, a method of forming such a laminate sheet,and a formed body obtained from such a laminate sheet. Morespecifically, it relates to a biodegradable laminate sheet of apolylactic acid-family resin which is superior in heat resistance, shockresistance and formability, and which decomposes under a naturalenvironment, a method of forming such a laminate sheet, and a formedbody obtained from such a laminate sheet such as a food container suchas a cup or a tray, a blister packaging material, a hot-fill container,a plastic case, or a tray or a carrier tape for transporting electronicparts.

BACKGROUND ART

As a material for a food container such as a cup or a tray, a blisterpack, a container for hot-fill, a plastic case, or a tray or a carriertape for transporting electronic parts, polyethylene, polypropylene,polyvinyl chloride, polystyrene, polyethylene terephthalate, or the likehave been used. These plastic products or the like are generallydiscarded after use, so that disposal such as burning and burial whendiscarding after use poses a problem. Resins such as polyethylene,polypropylene and polystyrene are large in calorific value when burnt,so that they may damage incinerators during burning treatment, andpolyvinyl chloride produces harmful gas during burning.

On the other hand, for burial disposal, too, since these plasticproducts are high in chemical stability, they will barely decompose inthe natural environment and remain semipermanently in the earth, so thatthey will saturate the capacity of garbage disposal sites in a shorttime. Also, if discarded in the natural environment, they will mar thelandscape or destroy the life environment of marine lives or the like.

Therefore, from the viewpoint of environmental protection, in recentyears, studies and developments of biodegradable materials are beingactively done. As one of biodegradable materials that are gatheringattention, there is a polylactic acid. Since a polylactic acid-familyresin is biodegradable, hydrolysis proceeds naturally in the earth andwater, so that it becomes a harmless decomposed product. Also, since itis small in burning calorie, even if it is subjected to burningtreatment, it will not damage furnaces.

Further, since the starting material originates from a plant, it doesnot-resort to oil resources which is exhausting.

But a polylactic acid-family resin is low in heat resistance, and wasnot suitable for use at high temperature such as containers for heatedfoods or containers into which hot water is to be poured. Also, instoring or transporting polylactic acid-family resin sheets or theirformed bodies, the interiors of storages, transporting trucks and shipsoften reach high temperature in summer, so that problems of deformation,fusing, etc. occur.

As a technique for imparting heat resistance to a polylactic acid-familyresin, there is a method in which in a forming step, the heat resistanceis imparted by crystallizing a polylatic acid to a high degree in a moldby holding the mold near the crystallizing temperature of the polylacticacid-family resin (80-130° C.). But in this method, in order tocrystallize the formed polylactic acid in the mold, untilcrystallization is completed, the formed body has to be held in themold, so that the forming cycle becomes longer than during normalforming, and thus the manufacturing cost becomes high. Also, since it isnecessary to heat the mold, a heating facility is also necessary.

Also, there is a method in which heat resistance is imparted bypost-crystallizing a polylactic acid-family resin to a high degree byannealing it after forming. But in this method, in the process ofpost-crystallizing the formed body of a polylactic acid-family resin,the formed body may be deformed, so that problems arise in dimensionalaccuracy. Also, since a step for post-crystallizing is necessary, themanufacturing cost becomes high.

As another method of imparting heat resistance to a polylacticacid-family resin, there is known a method in which after making thestorage elasticity in a predetermined range by pre-crystallizing alactic acid-family polymer sheet by annealing, forming is carried out ina heated mold (see patent document 1). But in this method, too, in orderto obtain a heat-resistant formed body, it is necessary to keep thetemperature of the mold near the crystallizing temperature of thepolylactic acid-family resin (80-130° C.), and finish crystallization ofthe polylactic acid-family resin in the mold, so that a facility forheating the mold is necessary. Also, in this method, the forming cyclebecomes longer than during normal forming, so that the manufacturingcost becomes high.

Furhter, in the above-described method in which a polylactic acid-familyresin is crystallized, the formed body obtained by the growth ofspherutiles basically becomes opaque. Thus it is difficult to obtain aformed body having transparency.

On the other hand, as a technique regarding laminate sheets comprising apolylactic acid-family resin and a biodegradable aliphatic polyesterother than a polylactic acid-family resin, there are known laminatefilms of aliphatic polyester having a number-average molecular weight of10000 or over and polylactic acid-family resin (see patent document 2),and laminate films of polylactic acid-family resin and a biodegradablealiphatic polyester other than polylactic acid-family resin (see patentdocument 3).

(patent document 1) JP patent publication 8-73628

(patent document 2) JP patent publication 8-85194

(patent document 3) JP patent publication 10-6445

PROBLEM THAT THE INVENTION INTENDS TO SOLVE

But polylactic acid-family resin used as laminate films described in thepatent documents 2 and 3 are stretched ones, and the technical object isto improve the heat-sealability of packaging bags.

Therefore, the present invention has as its object to provide a formedbody which is superior in heat resistance, shock resistance,transparency and formability.

MEANS TO SOLVE THE OBJECT

As a result of conducting vigorous consideration to solve the aboveobject, it has been found out that by laminating a polylacticacid-family resin and a biodegradable resin other than a polylacticacid-family resin, various formings such as vacuum forming, air-pressureforming, vacuum air-pressure forming and press forming are possible, andalso a heat-resistant formed body is obtainable even without holding themold near the crystallizing temperature of the polylactic acid-familyresin (80-130° C.), and the present invention has been reached.

The invention concerning the biodegradable laminate sheet according tothe present application relates to a sheet having a non-stretchedpolylactic acid-family resin of which the crystallinity is 20% or lessand a biodegradable resin layer other than a polylactic acid-familyresin.

Further, as the biodegradable resin layer other than a polylacticacid-family resin, a biodegradable aliphatic polyester layer other thana polylactic acid-family resin of which the glass transition temperatureis 0° C. or less and which has the melting point of 80° C. or over maybe used.

Also, it may be formed of at least three layers, with the biodegradableresin layers other than a polylactic acid-family resin forming outerlayers, and the non-stretched polylactic acid-family resin layer beingat least one layer sandwiched between the outer layers.

Further, it may be formed of at least three layers, with thenon-stretched polylactic acid-family resin being outer layers, and thebiodegradable resin layers other than a polylactic acid-family resinbeing at least one layer sandwiched between the outer layers.

Also, the non-stretched polylactic acid-family resin and thebiodegradable resin layer other than a polylactic acid-family resin canbe laminated by co-extrusion.

Further, the biodegradable laminate sheet described above may be formedat a temperature equal to or higher than the melting point of thebiodegradable resin other than a polylactic acid-family resin.

BEST MODE FOR EMBODYING THE INVENTION

Below, embodiments of the present invention are described.

The biodegradable laminate sheet according to the present invention is alaminate sheet having a layer comprising a non-stretched polylacticacid-family resin of which the crystallinity is 20% or less, and a layercomprising a biodegradable resin other than a polylactic acid-familyresin.

The polylactic acid-family resin used in the present invention comprisesa polylactic acid-family polymer. The polylactic acid-family polymerincludes a homo-polymer of which the structural unit is L-lactic acid orD-lactic acid, i.e. poly (L-lactic acid) or poly (D-lactic acid), acopolymer of which the structural unit is both of L-lactic acid andD-lactic acid, i.e. poly (DL-lactic acid), or their mixture. Further, itmay be α-hydroxy carboxylic acid or a copolymer of diol/dicarboxylicacid.

As a polymerizing method for a polylactic acid-family polymer, any knownmethods such as condensation polymerization or ring-openingpolymerization may be used. For example, in a condensationpolymerization, it is possible to obtain a polylactic acid-familypolymer having an arbitrary composition by directlydehydro-condensation-polymerizing L-lactic acid, D-lactic acid or theirmixture.

Also, in a ring-opening polymerization, a polylactic acid-family polymeris obtainable by polymerizing a lactide, which is a cyclic dimer oflactic acid, while using a polymerization adjusting agent as necessary,using a selected catalyst. Among lactides, there are L-lactide, which isa dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid,and DL-lactide, which comprises L-lactic acid and D-lactic acid. Bypolymerizing them while mixing as necessary, a polylactic acid-familypolymer having an arbitrary composition and crystallinity is obtainable.

Further, for example, if it is necessary to improve heat resistance, assmall-amount copolymerizing components, a non-aliphatic dicarboxylicacid such as terephthalic acid, or a non-aliphatic diols such asethylene oxide addition products of bisphenol A may be used.

Still further, for the purpose of increasing the molecular weight, asmall amount of a chain extender such as a diisocyanate compound, anepoxy compound or an acid anhydride may be used.

As the other hydroxyl-carboxylic acid units to be copolymerized with thepolylactic acid-family polymer, an optical isomer of lactic acid(D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid),bifunctional aliphatic hydroxyl-carboxylic acids such as glycolic acid,3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid,2-hydroxy 3,3-dimethyl butyric acid, 2-hydroxy 3-methylbutyric acid,2-methyllactic acid, and 2-hydroxycaproic acid, and lactones such ascaprolactone, butyrolactone and valerolactone may be used.

As the aliphatic diol to be copolymerized with the polylacticacid-family polymer, ethylene glycol, 1,4-butane diol, 1,4-cyclohexanedimethanol or the like can be used. Also, as the aliphatic dicarboxylicacid, succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoicdiacid, or the like can be used.

But as for the composition ratio in the polylactic acid-family resin,the polylactic acid is the main body, and the molar % of lactic acid is50 molar % or over.

The preferable range of the weight-average molecular weight of thepolylactic acid-family polymer is from 50000 to 400000, preferably form100000 to 250000. If it is below this range, practicality will scarcelyreveal. If it exceeds, the melt viscosity would be too high, so thatformability is inferior.

The biodegradable resin other than a polylactic acid-family resin is aconstituent component for imparting heat resistance and shock resistanceto the biodegradable laminate sheet and its formed body of the presentinvention.

As the biodegradable resin other than a polylactic acid-family resin,polyesteramide-family resin, cellulose-family resin, biodegradablealiphatic-family polyester other than a polylactic acid-family resin,polyvinyl alcohol, polyurethane, or the like can be used.

As the polyester amide-family resin, a copolymer of caprolactone andcaprolactum can be used. Also, as the cellulose-family resin, celluloseacetate or the like can be cited.

As the biodegradable aliphatic-family polyester other than a polylacticacid-family resin, polyhydroxy carboxylic acid, aliphatic polyester oraliphatiec aromatic polyester obtained by condensing aliphatic diol andaliphatic dicarboxylic acid or aromatic dicarboxylic acid; aliphaticpolyester copolymer obtained from aliphatic diol and aliphaticdicarboxylic acid and hydroxycarboxylic acid; aliphatic polyestersobtained by ring opening polymerizing cyclic lactones; syntheticaliphatic polyesters; and aliphatic polyesters bio-synthesized in fungusbodies may be used.

As the polyhydroxy carboxylic acid, a homopolymer or a copolymer ofhydroxycarboxylic acids such as 3-hydroxybutyric acid, 4-hydroxybutyricacid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylebutyric acid,2-hydroxy-3-methylbutyric acid, 2-methyllactic acid or 2-hydroxycaproicacid may be used.

As the aliphatic diol, ethylene glycol, 1,4-butane diol, 1,4-cyclohexanedimethanol or the like may be used. Also, as the aliphatic dicarboxylicacid, succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoicdiacid, or the like may be used.

As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acidor the like may be used.

The aliphatic polyester obtained by condensing these aliphatic diols andaliphatic dicarboxylic acids, and the aliphatic aromatic polyesterobtained by condensing aliphatic diols, aliphatic dicarboxylic acids andaromatic dicarboxylic acids are obtained by selecting one or more kindfrom these compounds, and condensation polymerizing them. Further, asnecessary, by jumping-up with an isocyanate compound, a desired polymercan be obtained.

As aliphatic diols and aliphatic carboxylic acids used for an aliphaticpolyester copolymer obtained from aliphatic diols and aliphaticdicarboxylic acids and hydroxycarboxylic acids, ones mentioned above maybe used. Also, as hydroxycarboxylic acids, L-lactic acid, D-lactic acid,DL-lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyricacid, 2-hydroxy-n-butyric acid, 2-hydroxy 3,3-dimetyl butyric acid,2-hydroxy 3-methyl butyric acid, 2-methil lactic acid, 2-hydroxy caproicacid or the like may be used. For example, polybutylene succinate lacticacid, polybutylene succinate adipate lactic acid or the like may beused.

But as for the composition ratio in this case, aliphatic diol andaliphatic dicarboxylic acid are main bodies. For the molar %, aliphaticdiol: 35-49.99 mole %, aliphatic dicarboxylic 35-49.99 mole %, andhydroxylcarboxylic acid: 0.02-30 mole %.

The aliphatic polyester obtained by ring opening polymerizing a cycliclactone is obtained by polymerizing, as a cyclic monomer, one or morekind of ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone.

As the synthetic-family aliphatic polyester, a copolymer of a cyclicanhydride with an oxirane such as a copolymer of anhydrous succinic acidwith ethylene oxide or propylene oxide may be used.

As the aliphatic polyester biosynthesized in the fungus, an aliphaticpolyester biosynthesized by acetyl coenzyme A (acetyl CoA) in fungusrepresented by Alcaligenes eutrophus can be cited. The aliphaticpolyester biosynthesized in the fungus is mainly poly-β-hydroxybutyricacid (poly3HB). But in order to improve practical properties as aplastic, it is industrially advantageous to copolymerize hydroxyvalericacid (HV) into a copolymer of poly(3HB-CO-3HV). The HV copolymerizationratio is generally preferably 0-40 mol %. Further, instead ofhydroxyvaleric acid, long-chained hydroxyalkanoate such as3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxyoctadecanoate, or thelike may be copolymerized.

As specific examples of biodegradable aliphatic-family polyester otherthan a polylactic acid-family resin, at least one kind selected from thegroup consisting of polybuthylene succinate, polybutylene succinateadipate, polybutylene adipate terephthalate, polybutylene succinateadipate terephthalate, polybutylene succinate lactic acid, polybutylenesuccinate adipate lactic acid, polyester carbonate, a copolymer ofpolyhydroxybutyrate and polyhydroxyvalerate, and a copolymer ofpolyhydroxybutyrate and polyhydroxyhexanoate can be cited.

The crystallinity of non-stretched polylactic acid-family resin which isa constituent component of one layer of the biodegradable laminate sheetaccording to the present invention, is preferably 20% or less, morepreferably, 15% or less and further preferably 10% or less.

The method of suppressing the crystallinity of the non-stretchedpolylactic acid-family resin to 20% or less is not particularly limited.But for example, a method in which a sheet extruded by an extruder iscooled by a cooling roll such as a casting roll (at a temperature of15-60° C.) to suppress crystallization of the polylactic acid-familyresin, and a method in which the rate of D-lactic acid and L-lactic acidin the polylactic acid-family resin is adjusted and because a randomcopolymer in which the rate of L-lactic acid and D-lactic acid is about95:5 to 5:95 is low in crystallinity, such polylactic acid-familypolymers may be used.

If the crystallinity of the non-stretched polylactic acid-family resinlayer exceeds 20%, formability worsens. Thus general purpose formingsuch as vacuum forming or air-pressure forming becomes difficult. Also,if the crystallinity exceeds 20%, due to the growth of spherulites ofthe polylactic acid-family resin, the transparency will worsen.

For the crystallinity of the polylactic acid-family resin, its lowerlimit is not limited if it is 20% or less.

The polylactic acid-family resin layer is preferably a non-stretchedone. If a sheet obtained by stretching a polylactic acid-family resin isused, in order to obtain a formed body, excessive pressure of e.g. about9 kg/cm² is necessary, so that forming at low pressure such as vacuumforming will be difficult. Also, since a stretched sheet needs an extrastep of stretching compared to a non-stretched one, it isdisadvantageous in cost too.

The glass transition temperature of the biodegradable resin other than apolylactic acid-family resin which is a constituent component of theother layer of the biodegradable laminate sheet according to the presentinvention is preferably 0° C. or lower, and more preferably −20° C. orlower. If high than 0° C., the improvement in the shock resistance isinsufficient. Also, the lower limit of the glass transition temperatureis not particularly limited, but is preferably practically −60° C. ormore. With a material of which the glass transition temperature is lowerthan −60° C., the melting point will be lower than 80° C., so that theheat resistance may be insufficient.

Also, the melting point of the biodegradable resin other than apolylactic acid-family resin has to be 80° C. or over. If the meltingpoint is less than 80° C., the heat resistance of the formed body may beinsufficient. Also, the upper limit of the melting point is notparticularly limited, but from the viewpoint of formability, it ispreferably 170° C.

The layer comprising the biodegradable resin other than a polylacticacid-family resin may be a stretched one or a non-stretched one, but asdescribed above, from the cost aspect, a non-stretched one ispreferable.

The thickness of the biodegradable laminate sheet of the presentinvention is not particularly limited, if it has such a thickness thatit can be used for a normal heat forming technique. But normally, thetotal thickness is preferably in the range of 0.07-2.0 mm.

Also, the ratio of the thickness of the layer comprising thebiodegradable resin other than a polylactic acid-family resin to thethickness of all the layers is 0.005-0.7. Specifically, the thickness ofthe layer comprising the biodegradable resin other than a polylacticacid-family resin is preferably 0.003-0.1 mm, more preferably 0.005-0.05mm.

The thickness of the layer of a polylactic acid-family resin is athickness obtained by subtracting the thickness of the layer comprisingthe biodegradable resin other than a polylactic acid-family resin fromthe total thickness.

The biodegradable laminate sheet of the present invention will do if itcontains at least two layers, i.e. a non-stretched polylacticacid-family resin layer and a layer comprising the biodegradable resinother than a polylactic acid-family resin.

Further, if the biodegradable laminate sheet of the present invention isformed of at least three layers, one layer is outer layers, and theother layer is at least one layer sandwiched by the outer layers.Specifically, the layer comprising the biodegradable resin other than apolylactic acid-family resin forms the outer layers, and thenon-stretched polylactic acid-family resin layer is at least one layersandwiched by the outer layers, or alternatively the non-stretchedpolylactic acid-family resin is the outer layers, and the layercomprising the biodegradable resin other than a polylactic acid-familyresin may be at least one layer sandwiched by both of the outer layers.

Also, so long as the object of the present invention is not impaired,end materials produced during the manufacturing process may be mixed inthe other layer for recycling.

The method of manufacturing the biodegradable laminate sheet of thepresent invention is not particularly limited if the object of thepresent invention is not impaired. But for example, {circle around (1)}a coextrusion method in which the polylactic acid-family layer and thelayer comprising a biodegradable resin other than a polylacticacid-family resin are laminated with a multi-manifold type or fieldblock type base using two or three or more extruders to extrude as amolten sheet, {circle around (2)} a method in which the one layer, whichhas been rolled out, is coated with the other resin, and {circle around(3)} a method in which the layers, which are at suitable temperatures,are hot-pressed using a roll or press, and {circle around (4)} a methodin which they are stuck together using an adhesive can be cited. But inview of ease of the manufacturing and the cost, the coextrusion methodis preferable.

The forming temperature for the biodegradable laminate sheet ispreferably the melting point of the biodegradable resin other than apolylactic acid-family resin or higher. If less than the melting point,the heat resistance and formability may be insufficient.

By forming the biodegradable laminate sheet according to the presentinvention by an arbitrary method such as by using a forming mold, aformed body is obtainable. As examples of the formed body, there arelunchboxes, trays and cups for foods such as fresh fish, meat, fruitsand vegetables, bean curds, household dishes, desserts and instantnoodles; packaging containers for toothbrushes, batteries, drugs,cosmetics, etc.; hot-fill containers for puddings, jam and curry;plastic cases having fold lines; or trays for transporting electronicparts such as ICs, transistors and diodes; and carrier tapes.

Further, for the biodegradable laminate sheet of the present invention,various modifications are possible by adding secondary additives. Asexamples of secondary additives, stabilizers, antioxidants, UVabsorbers, pigments, antistats, conductive agents, release agents,plasticizers, perfumes, antimicrobials, nucleation agents, and othersimilar ones can be cited.

EXAMPLES

Below, by showing manufacturing examples, examples and comparativeexamples, the present invention will be described in detail, but thepresent invention is not limited whatsoever. Physical values in Examplesand Comparative Examples were measured and evaluated by the followingmethods.

♦ Heat Resistance

For formed bodies obtained from biodegradable laminate sheets, aftercarrying out heat treatment for 20 minutes at 80° C. using a hot aircirculation type oven (FC-610 made by Advantec Toyo Kaisha, Ltd.), theywere let to cool to 23±2° C. The heat-treated formed bodies were put inwater of 23±2° C. with the volume of the water filling the formed bodiesmade as the volume (internal volume) of the formed bodies. On the otherhand, water of 23±2° C. was put into formed bodies which were left at23±2° C. without carrying out heat treatment, and the volume of thewater filling the formed body was made as the volume (internal volume)of the formed bodies before heat treatment. Using them, the volumereduction ratio of the formed bodies was calculated from the followingformula.Volume reduction ratio={1−(volume of formed body after heattreatment/volume of formed body before heat treatment)}×100♦ Shock Resistance

Using Hydroshot shock tester Model HTM-1 made by Toyo Seiki Co., Ltd.,at temperature 23° C., a firing core having a diameter of ½ inch wascollided against the biodegradable sheets at a speed of 3 m/sec. and theenergy needed to destroy it was calculated.

♦ Crystallizing Temperature

Under JIS-K-7121, using differential scanning calorimetry (hereinafterDSC), ΔHm and ΔHc attributable to polylactic acid-family resin inbiodegradable sheet were determined at the temperature rising speed of10° C./min, and the crystallizability of polylactic acid-family resinwas calculated by use of the following formula:

Cristallinity:xc%=(ΔHm−ΔHc)/(92.8× content of polylactic acid-family resin insheet)×100♦ Melting Point

Under JIS-K-712, under differential scanning calorimetry (DSC), themelting point was measured at the temperature rising speed of 10°C./min.

♦ Formability

Using a forming mold (mold temperature 25° C.) of 100 mm dia, depth 30mm, drawing ratio of 0.3, vacuum forming (vacuum pressure: −70 cmHg) wasdone, and the shape imparting state of the formed bodies was observed.

Haze

Measurements were made under JIS-K-7105.

Example 1

15 ppm of tin octylate was added to 100 kg of L-lactide (trade name:PURASORB L) made by PURAC JAPAN, and the mixture was put in a 500-literbatch type polymerization tank having a stirrer and heater. Nitrogenreplacement was carried out, and polymerization was carried out for 60minutes at 185° C. at the stirring speed of 100 rpm. The molten resinobtained was fed into a 40 mm dia. same-direction, two-shaft extruderhaving vacuum vents in three tiers and made by Mitsubishi HeavyIndustries, Ltd. and extruded in strands at 200° C. while degassing at avent pressure of 4 torr to pelletize it, and dried at 70° C. for 24 hr.The weight-average molecular weight of the polylactic acid-family resinobtained was 200000, and the L-body content was 99.5%. The melting pointmeasured under DSC was 171° C.

The pellets obtained were fed to a 65 mm dia. single-shaft extruder, andwere extruded through a multi-manifold type base at 200° C. for anintermediate layer.

Also, simultaneously, dried pellets of polybutylene succinate adipate(BIONOLLE made by Showa Highpolymer Co., Ltd. melting point: 95° C.,glass transition temperature: −40° C.) as a biodegradable resin otherthan a polylactic acid-family resin were fed into a 32 mm dia.single-shaft extruder, and were extruded through a multi-manifold typebase at 190° C. for front and back layers. At this time, the extrudingamount was adjusted so that the thickness ratio of the front layer,intermediate layer and back layer would be about 1:28:1.

The extruded molten sheet was brought into contact with a cast roll at40° C., and a biodegradable laminate sheet 300 microns thick wasobtained. The crystallinity of the polylactic acid-family resin of thebiodegradable laminate sheet obtained was 9%.

Next, using the biodegradable laminate sheet obtained, a formed body wasformed. That is, using a forming mold (mold temperature 25° C.), vacuumforming was carried out at the sheet temperature of 100° C., vacuumpressure of −70 cmHg to obtain a biodegradable formed body. The formedbody obtained was evaluated in heat resistance, shock resistance,formability and haze at 80° C. for 20 min. The results thereof are shownin Table 1.

Example 2

Except that the thickness ratio of the front layer, intermediate layerand back layer was changed to 1:8:1, a biodegradable laminate sheet wasobtained in the same manner as in Example 1. The crystallinity of thepolylactic acid-family resin of the biodegradable laminate sheetobtained was 8%.

Also, using the biodegradable laminate sheet obtained, a formed body wasobtained in the same manner as in Example 1. The formed body obtainedwas evaluated as in Example 1. The results thereof are shown in Table 1.

Example 3

Except that the thickness ratio of the front layer, intermediate layerand back layer was changed to 1:4:1, a biodegradable laminate sheet wasobtained in the same manner as in Example 1. The crystallinity of thepolylactic acid-family resin of the biodegradable laminate sheetobtained was 8%.

Also, using the biodegradable laminate sheet obtained, a formed body wasobtained in the same manner as in Example 1. The formed body obtainedwas evaluated as in Example 1. The results thereof are shown in Table 1.

Example 4

The biodegradable resin other than a polylactic acid-family resin usedin Example 1 was fed to a 65 mm dia. single-shaft extruder, and extrudedthrough a multi-manifold type base at 190° C. for the intermediatelayer.

Also, simultaneously, the polylactic acid-family resin used in Example 1was fed to a 32 mm dia. single-shaft extruder, and extruded through amulti-manifold type base at 200° C. for front and back layers. At thistime, the extruding amount was adjusted so that the thickness ratio ofthe front layer, intermediate layer and back layer would be 2.5:1:2.5.

The extruded molten sheet was brought into contact with a cast roll at40° C., and a biodegradable laminate sheet 300 microns thick wasobtained. The crystallinity of the polylactic acid-family resin of thebiodegradable laminate sheet obtained was 7%.

Also, using the biodegradable laminate sheet obtained, a formed body wasobtained in the same manner as in Example 1. For the formed bodyobtained, the same evaluations as in Example 1 were carried out. Theresults thereof are shown in Table 1.

Example 5

Except that as the biodegradable resin other than a polylacticacid-family resin, polybutylene succinate (BIONOLLE made by ShowaHighpolymer Co., Ltd. melting point: 111° C., glass transitiontemperature: −40° C.) was used, a biodegradable laminate sheet wasobtained in the same manner as in Example 1. The crystallinity of thepolylactic acid-family resin of the biodegradable laminate sheetobtained was 8%.

Also, the biodegradable laminate sheet obtained was subjected to vacuumforming at the sheet temperature of 120° C., and the vacuum pressure:−70 cmHg to obtain a biodegradable formed body.

For the formed body obtained, the same evaluations as in Example 1 werecarried out. The results thereof are shown in Table 1.

Example 6

15 ppm of tin octylate was added to 90 kg of L-lactide (trade name:PURASORB L) made by PULAC JAPAN, and 10 kg of DL-lactide (trade name:PURASORB DL) made by the same company, and the mixture was put in a500-liter batch type polymerization tank having a stirrer and a heater.Nitrogen replacement was carried out, and polymerization was carried outfor 60 minutes at 185° C. at the stirring speed of 100 rpm. The moltenarticle obtained was fed into a 40 mm dia., same-direction, two-shaftextruder having vacuum vents in three tiers and made by Mitsubishi HeavyIndustries, Ltd. and extruded in strands at 200° C. while degassing atthe vent pressure of 4 torr to pelletize it, and dried at 70° C. for 24hr.

The weight-average molecular weight of the polylactic acid-family resinobtained was 200000, and the L-body content was 94.8%. The melting pointmeasured by DSC was 165° C.

Except that the pellets obtained were used, a biodegradable laminatesheet was obtained in the same manner as in Example 1. The crystallinityof the polylactic acid-family resin of the biodegradable laminate sheetobtained was 4%.

Also, using the biodegradable laminate sheet obtained, a formed body wasobtained in the same manner as in Example 1. For the formed bodyobtained, the same evaluations as in Example 1 were carried out. Theresults thereof are shown in Table 1.

Comparative Example 1

The polylactic acid-family resin used in Example 1 was fed to a 65 mmdia. single-shaft extruder, and extruded through a base for a singlelayer at 200° C. The extruded molten sheet was brought into contact witha cast roll of 40° C. to obtain a polylactic acid-family resin singlesheet 300 microns thick. The crystallinity of the polylactic acid-familyresin of the biodegradable laminate sheet obtained was 8%.

Also, using the biodegradable laminate sheet obtained, a formed body wasobtained in the same manner as in Example 1. For the formed bodyobtained, the same evaluations as in Example 1 were carried out. Theresults thereof are shown in Table 1.

Comparative Example 2

The biodegradable laminate sheet obtained in Example 1 was subjected toheat treatment in a hot-air oven at 80° C. for 24 hours. Thecrystallinity of the polylactic acid-family resin of the biodegradablelaminate sheet obtained was 33%.

Also, using the biodegradable laminate sheet obtained in Example 1, aformed body was obtained in the same manner as in Example 1. For theformed body obtained, the same evaluations as in Example 1 were made.The results thereof are shown in Table 1.

Comparative Example 3

For the biodegradable laminate sheet obtained in Example 1, vacuumforming was carried out at a sheet temperature of 75° C. and vacuumpressure of −70 cmHg to obtain a biodegradable formed body.

For the formed body obtained, the same evaluations as in Example 1 wascarried out. The results thereof are shown in Table 1.

RESULTS

As shown in Table 1, Examples 1-6 were satisfactory in heat resistance,shock resistance and formability, and good results were obtained. Forones in which the rate of the layer comprising the biodegradable resinother than a polylactic acid-family resin was low, transparency was goodtoo.

On the other hand, in Comparative Example 1, since there is no layercomprising a biodegradable resin other than a polylactic acid-familyresin, the results were poor in heat resistance and shock resistance.

In Comparative Example 2, since the crystallinity of the polylacticacid-family resin was high, the shape imparting properties of the formedbody were insufficient and there was no transparency either.

In Comparative Example 3, since it is formed at a lower temperature thanthe melting point of the biodegradable resin other than a polylacticacid-family resin, the product showed poor heat resistance, and theshape imparting properties were not sufficient either.

EFFECT OF THE INVENTION

As described above, in the present invention, by using a laminate sheetcomprising a polylactic acid-family resin and a biodegradable resinother than a polylactic-acid family resin for forming, it is possible toprovide a formed body superior in heat resistance, shock resistance,transparency and formability by using a polylactic acid-family which iscapable of various formings such as vacuum forming, air-pressureforming, vacuum air-pressure forming and press forming.

TABLE 1 Comp. Comp. Comp. unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 1Ex. 2 Ex. 3 front & back resin — B B B A B B A B B layer thickness μ 10each 30 each 50 each 125 each 10 each 10 each — 10 each 10 each middlelayer resin — A A A B A A A A A thickness μ 280 240 200 50 280 280 — 280280 sheet thickness μ 300 300 300 300 300 300 300 300 300 front & backlayer/whole layer — 0.07 0.2 0.33 0.17 0.07 0.07 0 0.07 0.07 thicknessratio (μ) Crystalinity % 9 8 8 7 8 4 8 33 9 Forming temp. ° C. 100 100100 100 120 100 100 100 75 Heat Volume % 1.5 1 0.5 1.1 0.8 1.1 85 1 31.5resistance reduction ratio Shock resistance kgf · mm 15 25 50 24 14 15 417 15 Haze % 9 26 45 20 30 9 3 Unmeasurable 9 Formability — ∘ ∘ ∘ ∘ ∘ ∘∘ x Δ A: Polylactic acid-family resin B: Biodegradable resin other thanpolylactic acid-family resin Crystallinity: Crystallinity of polylacticacid-family resin in biodegradable laminate sheet Forming temperature:Temperature of biodegradable laminate sheet during forming

1. A method of forming a biodegradable laminate sheet which comprises anon-stretched polylactic acid-family resin layer of which thecrystallinity is 20% or less, and a layer comprising a biodegradableresin other than a polylactic acid-family resin having a glasstransition temperature of 0° C. or less and a melting point of 80° C. orhigher, wherein said method comprises forming said biodegradablelaminate sheet at a temperature higher than the melting point of saidbiodegradable resin other than a polylactic acid-family resin.
 2. Amethod according to claim 1, wherein said biodegradable laminate sheetcomprises outer layers comprising said biodegradable resin other than apolylactic acid-family resin, and at least one non-stretched layercomprising said polylactic acid-family resin sandwiched between saidouter layers.
 3. A method according to claim 2, wherein saidnon-stretched polylactic acid-family resin layer and said layercomprising a biodegradable resin other than a polylactic acid-familyresin are laminated by co-extrusion.
 4. A method according to claim 1,wherein said biodegradable laminate sheet comprises non-stretched outerlayers comprising said polylactic acid-family resin, and at least onelayer comprising said biodegradable resin other than a polylacticacid-family resin sandwiched between said outer layers.
 5. A methodaccording to claim 4, wherein said non-stretched polylactic acid-familyresin layer and said layer comprising a biodegradable resin other than apolylactic acid-family resin are laminated by co-extrusion.
 6. A methodaccording to claim 1, wherein said non-stretched polylactic acid-familyresin layer and said layer comprising a biodegradable resin other than apolylactic acid-family resin are laminated by co-extrusion.